Chaotic generation in a megawatt backward-wave tube

Experimental and theoretical studies on the self-modulation mode of generation in a high-power BWT with the electrodynamic system representing a slightly corrugated waveguide are presented. The BWT is fed by an electron beam with the energy 150 keV and the current 150 A. The system operates at the E ₀₁ mode with the mean frequency 8.7 GHz. Dynamic chaos is obtained by a three-fold increase in the length of the interaction space in comparison with the prototype exhibiting stationary generation. The stationary generation was changed to periodic sinusoidal self-modulation and then to chaotic self-modulation as the current increases from 6 to 60 A. The generation mode is simplified when the current ranges from 70 to 90 A and becomes complicated again for the current exceeding 100 A. Experimental observations are in good agreement with the results of simulation predicting a certain simplification of the self-modulation mode at the currents 70–90 A owing to the effect of high-frequency space charge. Under the conditions of chaotic generation, the mean power was as high as 2 MW at the relative spectral width of the signal 4% and the total duration of the microwave pulse 10 μs.     

Self-modulation oscillatory modes in a relativistic backward-wave oscillator

We present the results of numerical simulation of nonlinear dynamics in a relativistic backward-wave oscillator (BWO) over a broad range of parameters. A comprehensive study of the onset of self-modulation is carried out. It is found that the self-modulation boundary in the parameter plane has a complex shape. This is due to the competition between two different dynamical modes leading to the instability of single-frequency stationary oscillations. It is shown that the transition to chaos through period doubling bifurcations characteristic of a nonrelativistic BWO exists only for small values of the relativistic factor γ₀, while the transition through intermittency dominates for large γ₀. Higher College for Applied Sciences, State University of Saratov, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp.566–572, June 1999.     

Nonlinear quantum dynamics of two BEC modes dispersively coupled by an optical cavity

We derive a quantum master equation for a single mode excitation of a Bose-Einstein condensate by a high-finesse optical cavity. This system is formally analogous to a broad class of opto-mechanical systems comprising vibrating mirrors and resonator modes coupled by radiation pressure. The presented equation accounts for the dissipative part of the dynamics due to the coupling of a driven, lossy optical mode of a resonator. This allows for exploring the quantum limit of opto-mechanical systems in the presence of dissipation in a classically bistable regime. We find that the measurement-induced back-action noise impedes the observation of quantum tunneling and leads to a non-exponential dephasing of coherent matter wave oscillations.     

Dynamics of mode competition in the gyrotron backward-wave oscillator

The axial modes of the gyrotron backward-wave oscillator (gyro-BWO) each exhibit a distinctive asymmetry in axial field profile. As a result, and in sharp contrast to the behavior of the familiar resonator-based gyrotron oscillator, particle simulations of the gyro-BWO reveal a radically different pattern of mode competition in which a fast-growing and well-established mode is subsequently suppressed by a later-starting mode with a more favorable field profile. This is verified in a Ka-band experiment and the interaction dynamics are elucidated with a time-frequency analysis.     

Observation of chaotic dynamics in a powerful backward-wave oscillator

Self-modulation regimes of generation in a powerful 10-micros X-band backward-wave oscillator were studied theoretically and experimentally. The sequence of the self-modulation patterns and corresponding bifurcation values observed as the current was increased were in good agreement with the results of simulations. It was found that at a current of 120 A chaotic self-modulation set in at a power of 2 MW and a relative spectral width of 4%.     

Diffraction selection of modes in planar backward-wave oscillators

We study the possibility of obtaining spatially coherent radiation in a planar backward-wave oscillator fed with a wide sheet electron beam by using natural diffraction divergence of the radiation. This method is efficient for Fresnel parameters being approximately equal to unity. To solve the two-dimensional boundary problem, the spatio-temporal approach is used, which allows one to determine both the self-excitation conditions and the parameters of the stationary generation regime and the boundaries of its stability. The developed theory is used to evaluate the possibility of achieving diffraction synchronization of the radiation in a high-power planar backward-wave oscillator operated in the 8-mm wavelength band and based on a sheet relativistic electron beam produced by the U-3 accelerator of the Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.     

W波段损耗介质加载回旋返波振荡器中模式竞争的研究

本文采用自洽非线性理论模型系统研究W波段基波TE₀₁模回旋返波振荡器 模式竞争的物理机理. 通过采用特殊渐变的非谐振互作用结构和加载损耗介质抑制互作用系统中竞争模式, 从而防止系统出现非稳态振荡现象. 通过系统优化的互作用结构可以抑制竞争模式,能够稳定工作在TE₀₁模的轴向基模上. 计算表明系统输出峰值功率105 kW, -3 dB调谐相对带宽为5.4%. 这为发展应用于电子对抗、无损探测、等离子体诊断、材料处理等领域 的宽带毫米回旋返波振荡器提供了理论基础, 具有借鉴意义.     

螺旋线行波管返波自激振荡的研究

 在2维小信号模型的基础上，分析了均匀和周期永久聚焦磁场对抑制返波自激振荡的影响。研究结果表明：改变聚焦磁场的幅值或周期来增加起振长度是可能的， 而且不会改变基波的互作用条件。与此同时，对起振长度、初始非同步速度参量随皮尔斯增益参量、空间电荷参量、损耗参量等的变化，以及在超宽带行波管中当存在两个或多个角向非对称空间谐波时,起振长度、初始非同步速度参量随周期永久聚焦磁场的变化进行了研究。优化设计聚焦磁场、电子注和螺旋线慢波系统的参量可以对螺旋线行波管的稳定性分析提供必要的依据。     

螺旋线行波管返波自激振荡的研究

在2维小信号模型的基础上,分析了均匀和周期永久聚焦磁场对抑制返波自激振荡的影响。研究结果表明：改变聚焦磁场的幅值或周期来增加起振长度是可能的, 而且不会改变基波的互作用条件。与此同时,对起振长度、初始非同步速度参量随皮尔斯增益参量、空间电荷参量、损耗参量等的变化,以及在超宽带行波管中当存在两个或多个角向非对称空间谐波时,起振长度、初始非同步速度参量随周期永久聚焦磁场的变化进行了研究。优化设计聚焦磁场、电子注和螺旋线慢波系统的参量可以对螺旋线行波管的稳定性分析提供必要的依据。     

Synchronization of oscillations in a backward-wave tube: Theory and experiment

Synchronization of oscillations in an electron-wave system with a backward electromagnetic wave is studied theoretically and experimentally. The characteristics of nonautonomous oscillations in the backwardwave tube are analyzed with allowance for the space charge and physical processes accompanying the transition of the distributed autonomous system to the synchronization regime. Theoretical results are compared with experimental data.     

Nonlinear dynamics of two unstable waves

The dynamics of two interacting unstable waves is investigated. Possible stationary, homogeneous solutions for the amplitudes and their stability relative to the modulations are studied in the approximation of small, slowly changing amplitudes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 5–8, April, 1990.     

Effect of attenuation on backward-wave oscillation start oscillation condition

In a practical helix traveling-wave tube (TWT), there is always attenuator/sever for suppressing the oscillations, including backward-wave oscillation (BWO). The factors of the influencing BWO include start position of the attenuator, its length, and attenuation quantity. In the event that the attenuator/sever and nonuniformities in the phase velocity and beam potential were considered, a linear theory is employed to analyze BWO start oscillation condition. Numerical results show that the start oscillation length of the TWT decreases when the start position of the attenuator is close to the input section of the slow wave structure (SWS), that Start oscillation current of the output section of the SWS increases as the attenuation length decreasing, or the attenuation quantity increasing or the nonuniformities becoming strong, and that, however, when the phase velocity or beam potential exceeds a particular value, no oscillation condition could be found.     

Nonlinear domain-wall dynamics in a system of two magnetic layers

The nonlinear dynamics of the magnetization in a spin-valve structure is investigated. Equations describing the dynamics of the magnetization in such a structure are obtained. The stability of the solution corresponding to a motionless flat domain wall is investigated. The nonlinear domain-wall dynamics are investigated in the approximation of a strong exchange interaction between the magnetic layers and in the approximation of a large magnetostatic energy. In the former case the nonlinear dynamical equations are shown to be similar to the equations describing the dynamics of the magnetization in a weak ferromagnet, and in the latter case they are similar to the equations of motion of a magnetic vortex (i.e., a vertical Bloch line) in a domain wall. Zh. éksp. Teor. Fiz. 116, 1365–1374 (October 1999)     

Relativistic backward-wave tube with a smooth control over output radiation pulse duration

The effect of failure of oscillations in a low-impedance backward-wave tube is described and the possibility of using this effect for controlling the duration of output radiation pulses is considered.     

Relativistic backward-wave tube with nonuniform phase velocity of the synchronous harmonic

We have investigated the possibility of increasing the efficiency of a moderately relativistic backward-wave tube (BWT) by longitudinal modification of the phase velocity profile of the synchronous (−1) spatial harmonic. We have shown theoretically that the efficiency of oscillators with a nonuniform electrodynamic system may reach 60% in the approximation of a near zero space-charge field. We have found that the use of nonuniform periodic structures leads to reduction of the critical value of the space-charge field, and also impairment of the adaptive properties of the device. In our experiments, we have realized backward-wave oscillators (BWO) with 40% efficiency and microwave radiation power of 500 MW. Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 56–61, December, 1996.     

Nonlinear dynamics with higher-order modes in lithium niobate waveguide arrays

We present theoretical and experimental studies on nonlinear beam propagation in lithium niobate waveguide arrays utilizing higher-order second harmonic bands. We find that the implementation of the higher-order second harmonic bands leads to a number of new effects. The combined interaction of two second harmonic bands with a propagating fundamental beam can lead to a complete inhibition of nonlinear effects or to the formation of discrete spatial solitons, depending only on the wavelength of the fundamental wave. Furthermore we analyze the properties of discrete solitons, allowing for linear coupling of the second harmonic. Here we predict and demonstrate experimentally a power dependent phase transition of the soliton topology.     

Nonadiabatic dynamics of two strongly coupled nanomechanical resonator modes

The Landau-Zener transition is a fundamental concept for dynamical quantum systems and has been studied in numerous fields of physics. Here, we present a classical mechanical model system exhibiting analogous behavior using two inversely tunable, strongly coupled modes of the same nanomechanical beam resonator. In the adiabatic limit, the anticrossing between the two modes is observed and the coupling strength extracted. Sweeping an initialized mode across the coupling region allows mapping of the progression from diabatic to adiabatic transitions as a function of the sweep rate.     

Nonlinear modes of parametric vibrations and their applications to beams dynamics

An iterative loop combining nonlinear modes and the Rauscher method is suggested for analyzing finite degree-of-freedom nonlinear mechanical systems with parametric excitation. This method is applied to an analysis of the parametric vibration of beams.